1. Field of the Invention
This invention relates, in general, to a method and apparatus for continuously carrying out a gas phase reaction, and in particular, to an improved method and wave reactor apparatus for chemically synthesizing gases by subjecting them to compression and expansion waves.
2. Description of the Prior Art
The wave reactor is a relatively simple device in which gases are made to react with one another in a continuous manner by application of compression and expansion wave techniques. The unique characteristic of compression and expansion wave technology is that the gas which is subjected to the waves may be heated to extremely high temperatures very rapidly, and then cooled at extremely rapid rates with very precise control over reaction parameters. For industrial utilization, an ideal high-temperature chemical reactor must raise the reactant gas to the required reaction temperatures and cool the high temperature products fast enough so that there will be a minimum of product lost during the cooling process while at the same time minimizing circulating power losses and initial capital investment.
The background of the present invention may best be described with reference to one particular chemical reaction which may be carried out in accordance with the instant invention, namely, the fixation of nitrogen, hereafter simply termed NO, from air. Once nitrogen has been fixed as NO, the succeeding steps to the creation of nitric acid are relatively straightforward. Nitric acid is a well-established feedstock in fertilizer production. For example, the treatment of readily available limestone with nitric acid leads to the formation of "Norwegian Saltpeter", or, the treatment of ammonia leads to the creation of ammonium nitrate often considered one of the most useful forms of high concentration fertilizer. During World War I the Haber method of direct fixation of nitrogen was developed whereby nitrogen was combined with hydrogen under extreme pressures to form ammonia. With the birth of the great petroleum boom in the United States in the early post World War I years, the use of natural gas as a feedstock for the chemical industry was quickly exploited due to the ease with which natural gas could be used. In particular, methane was a source of cheap hydrogen, one of the chief requirements for the production of Haber ammonia.
By the end of World War II, the agriculture-chemical fertilizer industrial complex based on the Haber process had grown to the point where the United States was able to create a substantial oversupply of food. The combination of the progressively dropping price of fertilizer and the progressively sophisticated development of hybrid grains, particularly corn, appeared able to continue without limit. Nevertheless the alternative approach of fixing nitrogen from air, was pursued by a few visionaries, most notably Farrington Daniels. Daniels' concept involved heating air in a regenerative heat exchanger followed by a rapid quench to create high volumes of low concentration NO. Daniels' approach, however, was doomed to failure due to the technical limitations of the high temperature pebble-bed heater which he used and to the nearly violent expansion of the natural gas industry resulting in the creation of a market for natural gas in which this valuable and limited resource was literally given away at prices far below its equivalent energy value. It became clear that even for the production of nitric acid, Harber ammonia would compete economically with nitric acid produced from the fixation of air by the Farrington Daniels' approach and support for the Farrington Daniels' approach was withdrawn.
Between 1950 and 1960 the science and technology of high-energy gasdynamics was a fallout of the scientific developments created during World War II. Among these was the shock tube which presented to the scientists a convenient tool for the study of high temperature gas properties. A group at Cornell Laboratory which was involved in the study of nonsteady gasdynamics exhibited in shock tube type devices, began a serious set of investigations into the structure and nature of air at high temperatures. It was quickly realized by this group that at high temperatures, strong concentration of NO could be achieved directly by shock heating of gases. The concentrations, depending on the temperature, would easily exceed that of the heater reactor of Farrington Daniels and under optimal conditions could approach 5%. This possibility led to the development by this group of the device called the "chemical shock tube" which was specifically designed to create high temperature pulses in order to study the kinetics of the formation of NO as well as the necessity and appropriate mechanisms for retaining the equilibrium concentrations. Apparatus was designed and constructed for carrying out the gas phase reactions on a continuous basis, the apparatus designed being based in part upon a new class of machinery called the "comprex" which had been developed by Seippel as a device for improving the efficiency of gas turbine machinery. See Seippel U.S. Pat. No. 2,399,394. Abraham Hertzberg, one of the coinventors of the present invention, was personally involved in the work at Cornell and U.S. Pat. Nos. 2,832,666, 2,902,337, 2,930,196, 3,326,452 and 3,367,563, as well as Paper No. 66-GT-117 of the "Journal of Engineering for Power," substantially describe the nature and results of that work.
To summarize, the Cornell group conceived of a wave reactor apparatus which was designed to use compression forces generated therein to superheat a reactant gas, maintain the high temperature of the gas long enough to promote equilibrium formation and then suddenly cool the mixture by rapid expansion to preserve the desired equilibrium. By programing the wave processes, the apparatus was designed to recover as much of the desired reaction product as possible, consistent with the gasdynamics and working capability of machinery available at that time. In an NO formation reaction, the reacted air which had completed the high temperature portion of its cycle in the wave reactor left the reactor enriched with NO and was then further cooled by a regenerative heat exchanger. The driver cycle which carried out the function of a piston to compress the reactant gas was basically a system similar to that shown at the left-hand side of the broken lines 10 in FIG. 1 of this application as will be discussed in more detail hereinafter. In that system all make-up work was supplied by shaft power purchased off the line in the most convenient manner. This cycle proved to suffer from a number of dificiencies which led to excessive energy and capital requirements. In particular, the compressor and turbine components of the driver resulted in large circulating power losses and excessive capital investment. Nevertheless, this was a significant step beyond the Farrington Daniels' approach.
In a related project at Cornell, a large scale superheater facility was constructed which included a five foot diameter rotor drum with 288 individual shock tubes arranged around the circumference. This apparatus processed about five pounds of air per second at temperatures in excess of 4500.degree. K and is additionally discussed in the following articles:
W. e. smith and R. C. Weatherston, "Studies of a Prototype Wave Superheater," CAL Report No. HF-1056-A-1, AFOSR TR 58-158 AD 207244, December, 1958; PA0 A. h. flax, A. Hertzberg, and W. E. Smith, "A New Method for Providing Continuous High-Temperature Airflow for Hypersonic Research," CAL Report No. 79, AFOSR TN 56-236, May, 1956; PA0 R. c. weatherston, W. E. Smith, A. L. Russo, and P. V. Marrone, "Gasdynamics of a Wave Superheater Facility for Hypersonic Research and Development," CAL Report No. AD-118-A-1, AFOSR TN 59-107, February, 1959; and PA0 J. carpenter, "Engineering Design of a Wave Superheater Facility for Hypersonic Research and Development," CAL Report No. AD-1118-A-2, AFOSR TN 59-108. February, 1959.
Also of interest to the present invention are Hansel U.S. Pat. Nos. 3,272,598 and 3,254,960 and Hansel et al. U.S. Pat. No. 3,307,917 which disclose the heating and rapid cooling of gases other than air in a continuous flow shock tube process and the use of alternate drivers such as hydrogen to reduce the circulating power requirement.
In accordance with the instant invention, substantial process, method and apparatus improvements have been made in the above described wave reactor approach whereby both the circulating power and capital cost structure are radically improved.